1. Field of the Invention
This invention pertains to lithographic printing, and more particularly to dampening methods and apparatus associated with lithographic printing.
2. Description of the Prior Art
Conventional prior art dampening systems for lithographic printing presses are classed primarily as the continuous type or the semi-continuous ductor type, for which a dampening train of rollers makes direct physical contact with an initial dampening water input source on a full-time or part-time basis, respectively, and with a dampening form roller in contact with the lithographic printing plate. Certain recent dampening systems utilize a detached input of water by means of a spray or mist applied across a gap onto a receiving roller of the dampener train of rollers. Dampening systems with these detached or gapped water input means are termed discontinuous.
Other dampening systems such as the H. Dahlgren type in U.S. Pat. No. 4,527,479 and the Ghisalberti type in U.S. Pat. No. 4,461,208 use similar components to those just described but convey the dampening water to the plate by way of the first inking form roller instead of by means of a separate dampening form roller. In these indirect systems the first inking form roller actually becomes the dampening form roller. Special dampening water additives were found required for these systems to be acceptably operational.
In virtually all high-speed lithographic printing presses the dampening water is conveyed by means of a dampening train of rollers directly to the printing plate. By accumulating in the hydrophilic non-image regions of the plate, the water allows transfer of ink from the press inking form rollers only to the oleophilic image regions of the planographic lithographic printing plate. The resulting image differentiated inked regions of the plate are then transferred to a resilient blanket, then from the blanket to the substrate being printed.
In the practice of lithographic printing, nearly without exception, the dampening form roller is located prior to the first inking form roller and after the plate-to-blanket nip, as defined by the rotational direction of the printing plate. This practice is termed water-first dampening and the dominant prior art dampening configuration is termed the water-first, direct-to-plate, continuous type.
Dampening water conveyance to the plate by means of the inking train of rollers or by means of water-last, direct-to-plate dampening systems have been disclosed in the prior art and have been utilized in special types of lithographic presses, as, for instance, depicted in Fadner U.S. Pat. No. 4,690,055. These types have achieved limited commercial success and only in newspaper printing systems which have lower quality demands. Accordingly, both ink-train-dampening and water-last dampening have gradually been largely superseded in favor of conventional direct, water-first dampening systems and configurations.
The majority of installed high-volume lithographic printing presses around the world and virtually all of the high-volume lithographic presses currently being manufactured around the world utilize the dominant water-first, direct-to-plate continuous dampening configuration in one manifestation or another. All prior art dampening types suffer to a more or less significant degree from water interference with the transfer of ink to the printing plate. For instance, whenever the format to be printed contains low circumferential image content in one region of the plate at a given position of the overall press width and high circumferential image content in another cross-press location there exists no consistent prior art method, practice or apparatus to assure that dampening of the printing plate remains simultaneously trouble-free in both regions in regard to consistent and predictable ink input to the plate and thence to the substrate being printed. A similar situation occurs when changing from a low image content printing job to a high image content job or vice versa using the same printing press. A similar situation also occurs when switching from one ink type or source to another.
The inherent problems with these conventional dampening systems disallow consistent functioning of computerized inking systems. No known automated inking system can accurately be programmed for ink conveyance response to dampener-initiated printing system changes or disturbances because none of the prior art dampening methods can be accurately modeled to account for the disturbances. Even the most sophisticated computerized inking systems are not suitable for every printing condition because there exists no consistent prior art body of dampening technology that correctly allows or accounts for the influence of dampening upon the primary printing process function, which is inking.
This lack of dampening predictability is so pervasive that certain industry suppliers have developed waterless lithographic printing plates and presses in an attempt to obviate these ever-present dampening problems. Unfortunately, the waterless lithography approach requires exceptionally expensive inks, plates and presses. Also, waterless printing plates and presses are limited in the range of substrates that can be acceptably printed.
Fadner U.S. Pat. No. 5,107,762 depicts a lithographic printing process dampening system that utilizes initial dampening water input elements which are physically separated from a train of two or more direct-to-plate oleophilic and hydrophobic dampening water conveyance rollers, one roller of which is the dampening form roller contacting the printing plate. This dampening train of rollers becomes and remains partially inked during printing operations. The invention of the U.S. Pat. No. 5,107,762 patent was based solely on findings derived from keyless lithographic printing considerations. The disclosure therein is limited to the conventional direct-to-plate dampening configuration, which I have now discovered is not optimum for keyless lithographic printing and particularly not optimum for conventional keyed or zone inked lithographic printing systems. Currently, neither the 4,690,055 nor the 5,107,762 patent is being practiced or even tested using conventional key or zone inked lithographic presses. This is likely due to the preponderance of prior art lore and experience with zone or keyed printing presses that teaches against applicability of these patent technologies for conventional printing presses. I have now discovered that the technologies of these two patents are in fact not advantageously applicable to conventional lithographic presses.
The Dahlgren prior art dampening technology utilizes dampening water conveyance to the printing plate by direct roller contact of a dampening water input roller with the first inking form roller rather than by the more conventional means of an added dampening form roller contacting the plate. Having found that direct-to-plate dampening by means of an inking form roller was inoperable, Dahlgren uncovered that addition of rather large quantities of a water miscible organic liquid such as isopropyl alcohol to the dampening water remedied the practical problem that dampening water cannot be controllably carried directly to the printing plate by means of one or two inked rollers when one of the inked rollers is an inking form roller. In fact, the alcohol addition proved so useful in the practice of dampening that its incorporation pervaded the industry whether or not the dampener being used was of the Dahlgren type. This prior art background is summarized in Fadner U.S. Pat. No. 4,278,467, and the technical basis for alcohol's widespread acceptance is documented in "Surface Chemistry Control of Lithography." Colloids and Surfaces in Reprographic Technologies, by T. A. Fadner, ACS Symposium Series 200, pp. 348-57, M. Hair and M. D. Croucher, Ed., 1982.
Lithographic presses are easier to run and are more consistent, particularly as concerns ink/water interactions, when using 10 percent to 25 percent isopropanol in the dampening water. Substitutive additives for alcohol have by and large been unsuccessful in emulating this advantageous operational quality. In any case, all liquid organic material additives to the dampening water for this purpose are either highly or slightly volatile and are therefore environmentally and occupationally hazardous. The need remains to meet the advantageous operating influences of alcohol without necessity for use of any volatile organic compounds.
It is well known that to carry out conventional lithographic printing practices, two liquids are required, relatively viscous ink and relatively fluid dampening water. The viscous lithographic ink is essentially a non-volatile liquid insofar as the printing process is concerned. Consequently, excepting for mechanical losses, every bit of ink that is input to the press system is output by the press in the correct positions and amounts onto the substrate being printed. Conversely, water is an evaporative liquid under the pressroom operating conditions of temperature, pressure and room ventilation. Water will vaporize from and as vapor will generally move away from every operating press component upon which it is located.
It is also well known that lithographic ink can and must accept and tolerate some water within its continuous liquid film phase on press during lithographic printing operations. Water-proof inks are inoperable in the lithographic process and conventional lithographic printing is then not possible. Since all press rollers are manufactured to convey either water or ink, all roller and cylinder surfaces, whether hydrophobic or hydrophilic and whether or not ink covered will carry uppermost, normally molecularly thin, liquid/vapor water surface layers during printing operations. Water as vapor will be continually lost by evaporation away from all of these surfaces. In addition, liquid water will be lost by being printed out as part of the intended image of ink. Because of these natural and unavoidable water vapor and liquid water loss paths, considerably more dampening water must be input to a lithographic press system than would be required merely to replenish the natural water losses from only the printing plate non-image areas, which areas are the only locations where films of liquid water are appropriate on a continual basis while printing.
Water can and must enter the ink phase, and it is this interaction between water and ink that constitutes both the efficacy of lithography and the bane of lithography, the latter in terms of adverse effects of mechanically imposed or forced interactions related to press designs.
To achieve optimum lithographic efficiency relative to ink/water interactions, the press system must reach a water input-output equilibrium operating condition or steady-state appropriate for the speed, operating temperature, input rates of consumable ink and dampening water materials being used, and for the quality parameters of the product being manufactured. A slightly higher rate of dampening water input to the press than the equilibrium value will cause accumulation of additional water in the ink films residing on the various rollers, on the plate, and on the blanket. This system response must occur because water cannot evaporate faster from the various press components than the already established equilibrium rate, which is a natural response to ambient pressroom and press operating conditions. Consequently, under any water input rate condition just greater than this naturally occurring loss rate, the slightly excess water will be carried to the substrate by way of the ink being printed onto the substrate, and perhaps also by way of the non-image areas of press components that contact the substrate. The substrate path is the only natural path left for extra or excess water to exit the press system without noticeably adverse printed or operational quality disturbances.
When the dampening water input rate is further increased, a point is reached at which the thin ink films on the rollers cannot assimilate all of the increased water input. Free water may appear as more or less extended films on inked surfaces or at inked nips. A free water film can interfere directly with the intended smooth transfer of ink to the printing plate image areas and then to the substrate. This higher rate of water input is commonly referred to in the trade as exceeding the upper limit of ink/water balance latitude. The lower limit of ink/water balance latitude is, of course, the dampening water input rate which just fills all of the water loss paths of the press system. Below that rate of dampening water input, the inking form rollers will remove water from the printing plate non-image areas in order to fill the various inking rollers' surface evaporative demands, which loss paths had become water-starved under the low water input condition. When insufficient water remains in the non-image areas of the plate to prevent transfer of ink from the inking form rollers, the operating condition is termed toning or sometimes termed tinting. Ink will then reach the plate and therefore the substrate in areas corresponding to non-image regions that were supposed to remain unprinted and ink-free. All of the prior art conventional direct-to-plate dampening systems exhibit these water input faults to varying degrees. All of these prior systems in the absence of an alcohol additive are particularly sensitive operationally, having a narrow ink/water balance latitude range. With input efficiency faults of this kind, critical formats cannot be routinely printed at acceptable quality levels. Inking control systems cannot function as desired by design, trouble free.
To counter inefficient dampening water delivery to non-image areas of the plate, it is common printing practice for an operator to increase the dampening water input rate. Under this condition, water is lost not only to the natural printed out and evaporative paths but also by slinging and or misting loss of liquid water drops from the operating press components. When this occurs, product quality deterioration is usually observed because more water than lithographically necessary for image differentiation at the plate is being forced onto the press components and towards the plate and towards the substrate, all of which are adverse conditions. The press system may seem at times to be at a steady operating condition and acceptable printed quality is achieved momentarily because much of the detrimental excess water is slinging off from press components rather than interfering with the printing operation. However the system will vacillate out of and into acceptable printed output, requiring undue operator attention to fluid input rates and other mechanically controllable factors. There remains need for a press system that will function at the minimally required water input rates under all printing conditions thereby avoiding this very common continual operator adjustment paradox.
Any dampening water conveyance method or system that places a continuous or even a discontinuous but finite film of liquid water onto any roller that must transfer ink, particularly inking form rollers that contact the printing plate, are inherently inefficient dampening systems because the dampening system interferes with the primary function of the press, delivering ink to the plate. Relative to the ink's ability to imbibe or to pick up water at a nip with another roller, the natural water vapor film associated with press components can readily be exchanged to or from either or both rollers. The natural evaporative quantity of water vapor at a roller's surface does not constitute a barrier to transfer of either or both the ink or water from one roller to the next at their mutual nip. However, any liquid water film, no matter how thin, represents excess water most of which cannot be transferred into an ink film at a nip rapidly enough to disappear. Accordingly, any liquid water film represents a barrier to ink transfer. In fact, that is how lithography functions; by maintaining a finite thin film of liquid water in the non-image areas of the printing plate, allowing normal ink transfer only to the image regions of the plate. Whenever a finite film of liquid water appears between two inked surfaces more water than desired has been input to that nip. There will be poor ink/water balance latitude, poor operational control.
The ink/water balance latitude factor for a given lithographic press operating at a true lithographic equilibrium is therefore dictated in part by the ink's inherent ability to assimilate and distribute water towards all of the natural water loss paths. This dampening water distribution must be accomplished without significant change to nor interference with any of the critical quality properties of the ink. It is the intention of the present technology to do so.
As conventionally taught, lithographic printing problems are said to be dependent upon whether the printing plate is being overdampened or underdampened. While correct, this prior art statement is incomplete. It will become apparent in the present disclosure that optimum trouble-free dampening requires that none of the inking or dampening roller surfaces, as well as the printing plate surfaces, anywhere in the press system be overdampened or underdampened at any time during printing operations. The whole press inking system must be maintained at a steady operating state relative to the dampening water input rate. It will also become apparent that optimal lithographic dampening is coincident with minimal practical rate of dampening water input and therefore is automatically coincident with minimal number, variety and severity of the adverse ink/water interactions characteristic of prior art dampening systems.
Virtually all of the prior art dampening systems, which are of the direct-to-plate water-first type, are designed and tested to convey a continuous film of dampening water or dampening water solution towards the printing plate. The primary manifestation of this fact is the nearly universal practice of having a hydrophilic roller in the dampening input roller set to assure formation of a continuous water film thereon for subsequent direct conveyance to the plate by means of a dampening form roller. This practice renders the first inking form roller subsequent to the dampening form roller totally or at least largely incapacitated as an inking form roller. This readily demonstrated adverse condition follows logically from the fact that the first inking form roller subsequent in the printing plate rotational direction to the predominantly practiced water-first-dampening form roller configuration encounters at its nip with the printing plate a film of liquid dampening water that had to be input at a rate equivalent at least to the loss rate from all of the natural water loss paths, most of which are upstream in direction relative to the ink input, and not at a rate equal only to water losses from the plate. The dampening water input rates required for these systems is far greater than that which would be required merely to replace water losses from only the lithographically critical component, the printing plate. This required rate of dampening water input being forced in the prior art directly onto the printing plate is also greater than that which can readily be assimilated by the thin film of ink residing on the first inking form roller, merely by passing through its single, low-residence-time, narrow-nip with the printing plate. The reality of this condition is substantiated by the well known and demonstrable fact that when water-last direct-to-plate dampening is attempted, for which the dampening form roller is placed subsequent to the last inking form roller and therefore rotationally prior to the plate/blanket nip, transfer of ink from the plate to the blanket is completely lost or at best is nearly uncontrollable because of the water film forced onto the inked image areas on the plate by the water-last dampening system.
Since the ink film on the first inking form roller of, for instance, a set of four inking form rollers, cannot continuously carry away from the plate surface sufficient of the excess water input from the dampener, the second inking form roller may be affected similarly though less extensively. Perhaps also the third form roller. Each successive form roller is subjected to less excess water due to portions of the excess water having already been transferred by preceding form rollers towards the inking train of rollers water vapor loss paths. Finally, at the fourth or perhaps at the third inking form roller the water input to and from those rollers will closely approximate a natural water flow loss path equilibrium condition. One or both of the last inking form rollers will then be able to function properly and predictably as ink delivery rollers with little or no adverse interference from nor presence of liquid dampening water films on top of the ink that resides on the plate and on the contiguous rollers despite the excess dampening water initially input towards the printing plate.
Isopropyl alcohol assists the process of filling all the evaporative loss paths by rendering more efficient liquid water movement into and out of ink films. Thus, excess water, when present, is more readily removed from for instance the plate image areas by the inking form rollers, making the third and fourth, perhaps even the second form roller correspondingly more efficient in their intended roles as inking rollers. Under this condition of less liquid water interference with inking, a conventionally dampened press operates with less attention required to dampener related faults than without the alcohol additive. These factors explain the recent past virtual overall dependence on this additive that occurred over much of the industry.
When using for demonstration purposes a multiple inking form roller printing press carrying a printing format not subject to mechanical ghosting that normally could occur because of differing inking form rollers and plate cylinder diameters, it can be demonstrated that the printed ink density decreases markedly as the number of inking form rollers being employed is decreased, other factors being held constant. It is also well known that the last inking form roller, the one farthest from a conventional, direct, water-first dampening form roller, delivers during normal operation the smoothest and most water-interference-free ink film of the inking form roller set.
These observable factors using prior art practices are in part dampening design-related and secondarily inker-design related. Less than optimal inking conditions are the result of the inherently inefficient direct-to-plate conventional dampening practices which partially to severely negate what would otherwise be efficient conveyance of ink to the printing plate by all of the press system's inking form rollers. The excess rate of water input using these prior art conventional dampening systems coincides with the presence of one or more free liquid water films at the plate/inking form rollers' nips both in the image and the non-image regions of the plate.
The oleophilic and hydrophobic dampener roller system of U.S. Pat. No. 5,107,762 is advantageously functional for keyless inking lithographic systems. In keyless inking systems both the ink and the water inputs are continuously uniform across the press width. In conventional systems only the latter is input uniformly. In a keyless system, that portion of the ink not used by the plate, and coincidentally any water that has been mulled into the ink, is continuously scraped off the return side of an inking roller for reuse by the keyless press system. However, the dampener means of the U.S. Pat. No. 5,107,762 patent is not optimal nor perhaps even useful as the dampener input means for conventional zoned ink input printing presses wherein all of the ink being input must of necessity be printed out.
In practice, the oleophilic and hydrophobic dampening rollers of the U.S. Pat. No. 5,107,762 patent, being directly in liquid transfer contact with the plate, become ink covered only in circumferential bands located at cross-press positions directly corresponding to the cross-press locations of images on the printing plate. The greater the circumferential image content at any given cross-press location, the more complete is the corresponding circumferential ink film band observed on the dampener rollers, that is, the more likely that specific region will carry the maximum amount of ink possible, namely, that carried on average by the inking form rollers. Obviously, it is only these bands of ink on the dampener rollers that can participate in causing dampening water to mix into the ink for its non-interfering conveyance to the plate and this can occur only for the correspondingly located cross-press portions of the dampening water input which is being applied uniformly across the press width. Only these specific inked regions of the dampening rollers of the U.S. Pat. No. 5,107,762 patent can participate in what is termed in the present disclosure an admixture conveyance of dampening water and ink to the plate. Since normal overall image content varies up to about 50 percent coverage for most printing jobs, most of the U.S. Pat. No. 5,107,762 dampening roller surface area will not carry ink. The primarily uninked portions of the dampening system of the U.S. Pat. No. 5,107,762 patent operate exactly like a conventional direct-to-plate, non-inked dampening system with its inherent excess-water-induced interference with ink transfer. This adverse condition will be particularly severe with low image content formats, especially if attempts are made to utilize the U.S. Pat. No. 5,107,762 technology with conventional zoned inking presses where none of the input ink or water is being continuously removed as in keyless inking.
Prior art examples of attempts to obviate these pervasive dampening water interference problems in conventional presses include, for instance, the Alcolor Dampening system marketed by Heidelberger Druchmaschinen Aktiengesellschaft of Germany. A roller diagram reproduced from Heidelberg's April 1990 brochure titled M-Offset CP Tronic is illustrated together with the press inking rollers as FIG. 1. Dampening system 10 utilizes a differential speed nip 11 to meter a thin dampening liquid water film onto hydrophilic roller 12 which dampening water is then transferred in whole or in part as a liquid film to dampening form roller 13 thence to the printing plate mounted on cylinder 14. As in any printing press, the inking form and dampening form rollers must be covered with rubber or similar viscoelastic material because of mechanical and material considerations of their contact with the hard-surfaced printing plate. Rubber is naturally oleophilic and hydrophobic, therefore all form rollers on any press such as roller 13 in contact with an inked plate will normally tend to carry some ink. Ink will appear in differential cross-press regional amounts corresponding to image locations as just previously described herein for the U.S. Pat. No. 5,107,762 patent technology. Hydrophilic roller 15 is described to impart additional metering and/or smoothing action to the purposefully liquid, thin water film extending around and across roller 13. Oleophilic and hydrophobic copper roller 16 is somewhat unique for this otherwise conventional prior art dampening system in that it allows an inked roller bridge between form roller 13 and the inking system of rollers 16A by means of nip contact 17 with inking form roller 19. To the extent that ink transfers from roller 19 to roller 13 by means of roller 16, these may nearly operate as overall inked rollers in this particular system. Nevertheless, dampening form roller 13 must of necessity carry a more-or-less continuous water film on its surface.
This Alcolor bridge variation of the conventional, water-first, direct-to-press dampening method is consistent with my discovery of the inherent lithographic printing need that the water be purposefully mulled into the ink. However, the use of only one fully inked roller nip 17 between the water input source hydrophilic roller 12, and the first inking form roller 19 is far from sufficient to mull all of the input water into the ink even assuming that the relatively small volumes of ink on these rollers could accommodate all of the input ink required to fill all of the subsequent press component water loss paths without interfering with ink transfer. Consequently, but perhaps less severely than with non-bridged counterparts, the Alcolor system encounters all of the typically adverse lithographic water interference problems with inking that have already been described herein.
Other Heidelberg literature is consistent with this and other explanations herein. The manufacturer has modified the design of the inking train of rollers to automatically place considerably more ink on the first two inking form rollers than on the last two. Apparently, the combination of the Alcolor dampener and the extra ink input to the two form rollers that are exposed by the dampener to the greatest ink transfer water interference problems was found to improve press operations, particularly when inking has been computer automated (Heidelberg Speedmaster CD, CP Tronic, distributed publicly April 1993).
The Koromatic Dampener system marketed by Komori Corporation of Japan and illustrated in their July 1991 brochure titled New Lithrone is reproduced for use on their sheet-fed presses as FIG. 2. This direct-to-plate, continuous, water-first dampening system 20 utilizes a reverse slip nip 21 to meter a thin liquid water film onto the rubber dampening form roller 22 for subsequent transfer to the printing plate mounted on cylinder 23. This system employs an oleophilic copper roller 24 riding on rubber form roller 22, but unlike the Heidelberg system of FIG. 1, the Komori copper roller 24 does not bridge with inking system 25. As with the FIG. 1 system, a hydrophilic chrome roller 26 is required to prevent ink feeding back to water fountain 27 because of the direct connection between rollers 22, 26, 29, and 28 and is utilized to form a thin film of liquid water for transfer to the plate. If copper roller 24 is oscillated, the small amount of ink picked up by rubber dampening form roller 22 will be spread out somewhat, thereby nearly approximating the Heidelberg bridged roller advantage. However, typical prior art dampening interference with inking does and will persist for reasons already presented.
One prior art disclosure wherein the dampening water is conveyed indirectly to the plate by way of certain inking rollers and primarily by way of the first form roller, rather than totally or primarily by means of a direct-to-plate device typical of conventional prior art just described, is that of Ghisalberti in U.S. Pat. No. 4,461,208. This Ghisalberti technology is a variation of the Dahlgren technology already discussed herein and has the same faults and limitations.
As shown in FIG. 3, Ghisalberti utilizes chrome roller 5A to present a more or less uniform liquid dampening water film thereon for transfer in whole or in part as a liquid film to metering roller 6A which roller's surface composition is not specified. The latter may be assumed to be rubber, therefore oleophilic, because it must contact two hard-surfaced rollers, namely chrome roller 5A and inking transfer roller 7A of inking roller system 110. During operation, roller 6A will become mostly liquid water film covered because of its function as a dampening water distributing roller, despite the fact that it might also carry an ink layer beneath the water film that had been distributed to it in an upstream manner from inked transfer roller 7A. The transferred film of dampening water is reportedly milled into the ink during its transfer delivery by the inking system rollers to the plate by means of nips 111, 112 and 113 made with the inking distribution roller 7A and form rollers 8A and 9A. Obviously, milling, mixing action between water and ink at the plate/form roller nips would be counterproductive to image differentiation. Consequently, the form roller/plate nips cannot be considered primarily as water-into-ink-milling nips. Thus, this configuration provides at best two roller nips 111 and 112 that carry ink between the dampening water source roller 6A and the first ink form roller 8A and three such nips 111, 112 and 113 to form roller 9A.
The structure of the Ghisalberti technology does not recognize that a steady state water content must be achieved at all of the operating inking rollers of inking system 110 as well as at the plate 114 itself, as disclosed and discussed elsewhere herein. The FIG. 3 and related Ghisalberti reference drawings place the dampening water input at a press location where much of the input water must be conveyed upstream from the input roller 6A and from inking form roller 8A, in a direction away from the plate where the water is primarily required, while the ink is being conveyed downstream towards the plate, in order to fill the water vapor loss paths associated with all of the rollers between transfer roller 7A and form rollers 10A and 11A. Consequently, as with water-first dampening, more dampening water than minimally necessary for image differentiation at the plate must be continuously input to and be carried by the thin ink film on roller 7A, therefore also by that on rollers 8A and 9A. Water interference problems are to be expected similar to those encountered with Dahlgren dampening structures particularly in the absence of alcohol, as with the Heidelberg and Koromatic examples and the like already discussed herein. This prediction is verified accurate by the fact that Ghisalberti technology is not operational as just described. It requires and is limited by the patentee to the conditional use of the relatively large volumes of isopropyl alcohol in the dampening water, namely about 10% to 30% or more to be operational, as also required by the Dahlgren indirect to plate system herein previously discussed.
Graphic Systems Division of Rockwell International Corporation, a domestic company, marketed lithographic presses to newspaper printers which included what were termed ink train dampening systems (ITD) shown schematically in FIG. 4. This unpatented dampening configuration was prompted by customer demand that dampening components be readily accessible on the indicated side of the inking train of rollers for cleaning and maintenance. The dampening system 30 has a separated brush spray water input 31 which system is easy to clean. Input is to an inked roller 32 riding on a first copper inking drum 33 of the inking system 34. This system functioned reasonably well but there are at best only two or three nips carrying both ink and water between the receiving roller 32 and the inking form rollers in contact with the plate, as indicated numerically in FIG. 4, to mull water into the ink on its way to the plate. Also, the ink films on rollers 32 and 33 which need to convey all of the dampening water input are relatively thin, as in the Ghisalberti case, hardly capable of continuously handling all of the water that needs to be input to the press system. Although water input is primarily and advantageously in the ink downstream direction of travel towards the plate, field experience relative to increased demand for improved printed quality due to adverse ink/water interactions prompted gradual withdrawal of this system in favor of the more effective conventional direct-to-plate dampening systems.
There remains need for a consistent, repeatable, predictable, and efficient means for conveying to a lithographic plate the water required to maintain image differentiation at the plate without introducing significant adverse influence of the dampening water on the delivery of ink to the image area of the plate.